1. Field of the Invention
The present invention relates to an apparatus for connecting leads to lead frames, etc. and more particularly to an apparatus for bonding external leads of solid-state devices punched out from a film carrier to lead frames, substrates, etc.
2. Prior Art
An apparatus which connects external leads to lead frames, substrates, etc. works basically as follows: First, a solid-state device 2 (shown in FIG. 11) supported by external leads 2a on a film carrier 1 having sprocket holes 1a on both sides thereof is first punched out. The thus punched-out solid-state device 2 is positioned so that the leads 2a are aligned with lead connecting parts 3a or 4a of a lead frame 3 (shown in FIG. 12) or substrates 4 (shown in FIG. 13), respectively. The leads 2a are then bonded to the lead connecting parts 3a or 4a (as shown in FIGS. 14 and 15) to complete the entire connecting process.
Throughout the specification, the term "lead frames" refers not only to lead frames 3 but also to substrates 4.
Conventional apparatuses for connecting external leads can generally be divided into two types.
In the first type, a film carrier and lead frames are positioned so that the lead frames are laid over the film carrier. The solid-state devices on the film carrier are punched out, and at the same time, the thus punched-out solid-devices are bonded by heat and pressure to lead frames located overhead.
In the second type of apparatus, the film carrier and lead frames are positioned side by side. The solid-state devices on the film carrier are punched out, picked up by vacuum suction adhesion and then transferred to the lead frames. In this apparatus, bonding is accomplished by a separate bonding apparatus.
The above-described apparatus (the first type) is mainly for handling solid-state devices which have a small number of leads. If the solid-device device has a great number of leads, a higher degree of precision is required to position the leads exactly on the solid-state device and the lead frame. Accordingly, the positioning of this apparatus in which the lead frames are merely superimposed on the film carrier causes frequent positioning errors and the yield drops conspicuously. Furthermore, it is difficult to monitor the lead frames and film carrier separately. Thus, the precision of positioning tends to be poor.
On the other hand, in the second type of apparatus, a difficult question rises as to how the solid-state devices (which are punched out of the film carrier) are to be fixed in place on the lead frames. To solve this problem, several different methods are employed. For example, in one method, the solid-state device is temporarily held and set in the proper position on the corresponding lead frame. Then, the leads on each side of the solid-state device are bonded in separate steps via a bonding tool that is arranged so as not to interfere the temporary positioning of the solid-state device.
In another method, each punched-out solid-state device is placed on the lead frame without it being temporarily held, and the leads on the respective sides of the solid-state device are all bonded at the same time.
However, these methods have their drawbacks in that if the bonding process is divided into several steps, working efficiency becomes poor. On the other hand, the precision of the position doing the bonding tends to decrease if the bonding is performed without the solid-state devices being held temporarily.